1. Field of the Invention
The present invention relates to an ink jet recording head in which a bubble is generated by heating ink by means of an electrothermal converting element and the ink is discharged by pressure upon generation of the bubble, an ink jet recording head cartridge in which such an ink jet recording head and a liquid container for supplying liquid to the ink jet recording head are integrally formed, and an ink jet recording apparatus to which such an ink jet recording head cartridge is mounted.
2. Related Background Art
Almost all of ink jet recording apparatuses have been used as a printing apparatus in an image forming apparatus such as a printer, a facsimile, a word processor, a copying machine and the like. Among them, an ink jet recording apparatus of type in which thermal energy is used as energy utilized for discharging the ink and the bubble is generated in the ink by the thermal energy and the ink is discharged by change in volume upon generation of the bubble has recently been spread.
Further, as another application of the ink jet recording apparatus of this kind, an ink jet print device for printing a predetermined pattern, a design or a composite image on cloth has recently been known. An ink jet recording head used in the above-mentioned ink jet recording heads utilizes electrothermal converting elements (referred to also as xe2x80x9cheatersxe2x80x9d hereinafter) as means for generating the energy, and, in many cases, one heater corresponds to one discharge port.
To the contrary, an ink jet recording head in which a plurality of heaters are provided with respect to each of discharge ports for the following reasons has also been known.
That is to say, firstly, in order to extend the service life of the ink jet recording head, the plurality of heaters are driven alternately or the heater to be driven is appropriately switched. Secondly, by changing an ink discharged amount by selecting the heater or heaters to be driven, the change in ink discharged amount is realized.
As a concrete construction of the latter, an arrangement in which a plurality of heaters are disposed in each ink flow path (nozzle) communicated with a corresponding ink discharge port of the ink jet recording head along an ink discharging direction so that the ink discharged amount is changed due to the difference in distance between the driven heater and the associated discharge port by selecting the heater to be driven (heated) or the ink discharged amount is changed by changing the number of heaters to be driven has been known.
Further, as another construction, for example, as disclosed in Japanese Patent Application Laid-open No. 55-132259, an arrangement in which a plurality of heaters having different surface areas are disposed in each ink flow path so that the ink discharged amount is changed by similarly changing the heater to be driven or changing the number of heaters to be driven is also known.
An example of such an ink jet recording head is shown in FIG. 17 as a sectional view. As shown in FIG. 17, in this ink jet recording head, two heaters 6002, 6003 having different dimensions and different distances from a discharge port 6004 are disposed in a nozzle 6001 for communicating the ink discharge port 6004 with a common liquid chamber 6005 for containing ink to be supplied to a plurality of nozzles 6001 so that the amount of ink to be discharged can be changed by driving one or both of the heaters 6002, 6003.
Although the above-mentioned ink jet recording head having the plurality of heaters disposed in the respective nozzle has a purpose for realizing high speed and high accurate printing in response to various images by changing the ink discharged amount, there arose the following problem to achieve this purpose.
Nowadays, high density arrangement of the nozzle has been requested to achieve high accurate and finer printing, and, to this end, a width of each nozzle must be narrower. On the other hand, the heaters having large sizes must be used in order to widen the variable range of the ink discharged amount. Accordingly, when the size of the heater tries to be increased in the narrow nozzle, a longitudinal dimension (length) of each heater must be increased along the longitudinal direction of the nozzle, with the result that a length of the nozzle must be increased. If the length of the nozzle is increased, flow resistance of the nozzle will be increased, with the result that a time (re-fill time) for restoring meniscus retarded within the nozzle after the ink discharging to the vicinity of the discharge port again is delayed, thereby reducing the recording speed.
As a method for shortening the ink re-fill time to hasten the recording speed, a method in which the length of the nozzle 6001 is shortened, and, as shown in FIG. 18, a method in which a cross-sectional area of the nozzle 6001 at the heater 6002 is selected to be smaller than a cross-sectional area thereof at the inlet of the common liquid chamber 6005 (as disclosed in U.S. Pat. No. 4,752,787) are already known.
However, if the length of the nozzle is smaller than a certain value with respect to the heater position, when the temperature of the recording head is increased, a bubbling volume on the heater is increased, and the bubble formed by the bubbling may protrude from a rear end of the nozzle.
That is to say, as shown in FIG. 19A, even in case of a recording head a bubble 6007 is generated within a nozzle 6001 when the ink is bubbled in a condition that the recording head has a room temperature (for example, 25xc2x0 C.), when ink is generated in a condition that the temperature in the recording head is increased (for example, to about 60xc2x0 C. or more) due to discharging of ink from all nozzles with high frequency, since the energy required for the bubbling is small, if the energy similar to that shown in FIG. 19A is given, as shown in FIG. 19B, the bubble will be grown greatly to protrude toward the common liquid chamber 6005 from the nozzle 6001.
A state in which the ink is discharged in the condition that the temperature in the recording head is increased is shown in FIGS. 20A to FIG. 20E. FIG. 20A shows a condition that film boiling is started by heating the heaters 6002, 6003. From this condition, when the energy is further applied to the heaters 6002, 6003, the bobbles 6007 are grown as shown in FIG. 20B, with the result that the ink is discharged from the discharge port 6004 by pressure generated by the growth of the bubbles 6007. FIG. 20C shows a condition that the discharging of the ink is completed and the bubbles 6007 was grown to the maximum extent. In this condition, the bubble 6007 protrudes from the nozzle 6001 to reach the common liquid chamber 6005. From this condition, when the heating of the heaters 6002, 6003 is stopped to cool the bubbles 6007, contraction of the bubbles 6007 is started, and the re-fill of ink from the common liquid chamber is started and the ink near the discharge port is shifted, with the result that the meniscus starts to be retarded within the nozzle 6001. In the common liquid chamber communicated with the inlet of the nozzle, since the ink is flown into the nozzle at once around the bubble portion 6007 protruded in the common liquid chamber, eddy ink flow is created, with the result that, as shown in FIG. 20D, the bubble 6007 is separated. Thereafter, as shown in FIG. 20E, the bubbles 6007 on the heaters 6002, 6003 are disappeared, and the meniscus is restored in the vicinity of the discharge port 6004 as the ink re-fill continues. At this stage, the separated bubble 6007 remains within the common liquid chamber 6005.
Although the residual bubble 6010 remained within the common liquid chamber 6005 by single ink discharging in this way is small, when the ink is discharged from all of the nozzles with high frequency of about 10 kHz, a large amount of residual bubbles 6010 may be stored in the common liquid chamber for a short time. As shown in FIG. 21A, the stored or trapped residual bubbles 6010 is flown together with the ink during the ink re-fill to enter into the nozzle as shown in FIG. 21B, with the result that the complete ink re-fill may not be attained. Further, as shown in FIG. 21B, if the residual bubble 6010 covers the heater 6003, even when the heater 6003 is heated, a new bubble 6007 cannot almost be generated, with the result that the ink may not be discharged.
If the amount of residual bubbles in the common liquid chamber 6005 is small, although such residual bubbles can be removed by a suction recovery operation after the recording or during the recording, if the large amount of residual bubbles are generated for a short time, the suction recovery operation must be repeated frequently, with the result that an amount of useless ink sucked during the suction recovery operations is increased and the recording speed is worsened.
Further, if the nozzle 6001 is short, due to pressure energy transmitted from the rear end (connected to the common liquid chamber) of the nozzle 6001 to the common liquid chamber 6005 during the discharging of the ink droplet, a cross-talk phenomenon affecting a bad influence upon the ink discharging of the adjacent nozzle 6001 may occur.
Constructions of a nozzle 6001 suppressing or eliminating such bad influence such as poor discharging are shown in FIGS. 22A and 22B. In FIGS. 22A and 22B, for a purpose of comparison, the configuration of the nozzle 6001 of FIG. 17 is shown by the broken line.
In the construction shown in FIG. 22A, by lengthening the nozzle 6001, even when the bubbling is effected in the condition that the temperature in the recording head is increased, the bubble is prevented from protruding in the common liquid chamber 6005. However, with this construction, when the temperature in the recording head is high and viscosity of ink is low, although the short time re-fill can be achieved narrowly, if the temperature in the recording head is the room temperature, the re-fill time becomes very long and, thus, the recording with high frequency becomes impossible.
In the construction shown in FIG. 22B, by providing a restrict 6008 for restricting the flow cross-area at a rear end portion of the nozzle 6001 to increase flow resistance at the restrict (stricture), the bubble 6007 is prevented from growing toward the rearward of the nozzle 6001. However, in an arrangement in which the plurality of heaters 6002, 6003 are provided in the single nozzle 6001, there is the heater 6002 ahead of the rear heater 6003, and, by the bubbling action of the heater 6002, the bubble 6007 generated on the rear heater 6003 is pushed toward the rearward of the nozzle 6001. As a result, even when the flow resistance is increased at the rear portion of the nozzle 6001, the growing of the bubble 6007 toward the rearward of the nozzle 6001 cannot suppressed completely.
As mentioned above, in the ink jet recording head in which the plurality of heaters 6002, 6003 are provided in each nozzle 6001, sizes of areas on which the heaters are located become great in the longitudinal direction of the nozzle without fail. In this arrangement, if the length of the nozzle is increased, the re-fill time is increased; whereas, if the length of the nozzle is reduced, the residual bubbles are stored in the common liquid chamber 6005 and the stored residual bubbles flow back into the nozzle 6001 to generate the bad influence such as poor discharging. Thus, there is a xe2x80x9ctrade-offxe2x80x9d relationship.
Further, if the ink supplying ability is enhanced by approaching the common liquid chamber to the discharge port, even when the single heater is used, the bubble may protrude in the common liquid chamber. The present invention also solve such a problem.
Therefore, an object of the present invention is to provide an ink jet recording head which can overcome the conventional trade-off problem and in which the re-fill time is shortened and the residual bubbles are not stored in a common liquid chamber and a high quality image can be recorded at a high speed.
The other objects and features of the present invention will be apparent from the following detailed explanation of the invention.
In order to solve the above problems, the present invention provides an ink jet recording head comprising a plurality of discharge ports for discharging ink droplets, a plurality of ink flow paths communicated with the respective discharge ports, a common liquid chamber communicated with the ink flow paths and adapted to hold ink to be introduced into the ink flow paths, electrothermal converting portions disposed in the ink flow paths and adapted to generate heat for bubbling the ink, and bubble trapping portions disposed at communicating portion between the ink flow paths and the common liquid chamber and including stepped structures each having a cross-sectional area smaller than a main cross-sectional area of the common liquid chamber and greater than a cross-sectional area of the corresponding ink flow path in a direction perpendicular to an ink introducing direction, and wherein each of the ink flow paths is provided with an inclined portion located between an upstream end of the electrothermal converting portion and the communicating portion of the ink flow path with the common liquid chamber in the ink introducing direction and having a cross-sectional area, in the direction perpendicular to an ink introducing direction, gradually increasing toward the upstream bubble trapping portion, and a surface extended from the inclined portion intersects with a ceiling surface of the bubble trapping portion.
By providing such an inclined portion, even if a bubble formed on the electrothermal converting portion is grown rearwardly, since a volume at an upstream side of the electrothermal converting portion is great, the grown bubble can be prevented from protruding in the common liquid chamber, thereby preventing the bubble from being separated during ink re-fill.
Further, even if the bubble protrudes in the common liquid chamber, since a main direction of the ink in the re-fill is inclined along the inclined surface to reduce a difference between this direction and a flow direction of ink going round from above the protruded bubble, eddy current is hard to occur, with the result that the ink is re-filled smoothly without separating the bubble.
Further, since the cross-sectional area of the inclined portion in the ink introducing direction is great and the flow resistance at the inclined portion is small and since the ink flows smoothly in the re-fill, the ink re-fill time can be shortened.
In addition, since the ink jet recording head according to the present invention has the bubble trapping portion, the bubble discharged from the upstream end of the ink flow path can be trapped in the bubble trapping portion, thereby preventing the bubble from flowing back in the ink flow path. In the ink jet recording head having such bubble trapping portions, by the above-mentioned bubble trapping action and the action of the inclined portion for preventing the bubble grown rearwardly of the ink flow path from being separated and stored in the common liquid chamber, the residual bubble can be prevented from being stored in the upstream side of the ink flow path and can be prevented from flowing back in the ink re-fill.
In this case, by adopting the arrangement in which the surface extended from the inclined portion intersects with the ceiling of the bubble trapping portion, since the ink flow in the re-fill has a main flow component advancing substantially straightly toward the ink flow path in an area surrounded by a surface extended from a side surface in the ink flow path in the ink introducing direction, the ink is not almost supplied from the common liquid chamber to a zone near the ink flow path from the intersect portion between the surface extended from the inclined portion and the ceiling of the bubble trapping portion, with the result that the flow of ink at this zone can be reduced, and the residual bubble can be trapped at this zone, thereby preventing the residual bubble from flowing back into the ink flow path.
By applying the present invention to an ink jet recording head in which the plurality of electrothermal converting elements are arranged side by side in the ink introducing direction, and, when the plurality of electrothermal converting elements are driven substantially simultaneously, by the growth of the bubble formed on the downstream electrothermal converting element, the bubble formed on the upstream electrothermal converting element is pushed toward the upstream side to facilitate the growth of the bubble toward the upstream side of the ink flow path (common liquid chamber side), the above-mentioned problem caused by the remarkably rearwardly grown bubble can effectively eliminated.
Further, by providing the restrict having the small cross-sectional area in the direction perpendicular to the ink introducing direction at an upstream side of the upstream end of the upstream-most electrothermal converting element and at a downstream side of the inclined portion, even when ink having low viscosity is used, the ink in the re-fill can be flown at a proper speed, and the ink can be prevented from being discharged from the discharge port during the re-fill. Particularly, by selecting a relationship between the cross-sectional area S1 of the restrict in the direction perpendicular to the ink introducing direction and the cross-sectional area S2 of the restrict at the upstream end thereof to S1/S2xe2x89xa60.5, it is possible to bring the ink re-fill speed to an optimum value without generating eddy ink flow, thereby achieving this effect sufficiently.
In a case where it is assumed that an angle between the inclined portion and a surface on which the electrothermal converting element is located is xcex1 and an angle between the surface on which the electrothermal converting element is located and a surface connecting the upstream end of the upstream-most electrothermal converting element to an upper end of the rear end of the ink flow path is xcex2, if xcex1 is too small with respect to xcex2, in order to provide the arrangement in which the surface extended from the inclined portion intersects with the ceiling surface of the bubble trapping portion, it is required that the length of the bubble trapping portion be increased or the inclined portion be located at the downstream area form the upstream end of the electrothermal converting element. However, in the former case, the resistance in the suction recovery operation is increased not to effect the recovery sufficiently or lengthen the recovery time; whereas, in the latter case, the flow resistance rearwardly of the ink flow path becomes too small.
Further, if xcex1 is too great with respect to xcex2, the volume of the area where the ink is hard to flow in the re-fill as mentioned above will be reduced.
Thus, it is desirable that a relationship between xcex1 and xcex2 be selected to as follows:
xcex2xe2x89xa6xcex1 less than xcex2+10xc2x0.